Porosity has long been a problem responsible for reducing integrity of welds. Porosity is especially a problem when welding in an overhead welding position. During normal welding operations, large gas bubbles typically rise through liquid metal to escape the weld. However, during overhead welding operations, bubbles do not escape a weld by rising because upward movement is prevented by the base metal. Overhead welding requires a welding electrode that entraps an extremely low amount of gases. Furthermore, the slag must prevent excessive dripping of weld metal. An example of a flux specifically adapted for welding in the overhead position is disclosed by T. O. Bates in U.S. Pat. No. 4,940,882.
Using a flux to provide useful overhead welding conditions is not useful for every welding condition. For example with, some alloys which require a close match, it may not be practical to adjust the flux to solve porosity problems and maintain a desired weld deposit composition. There exists a need for a base metal that will facilitate overhead welding when using a variety of fluxes.
For example, the American Welding Society has developed stringent standards for ENiCrMo-6 welding electrodes. Minimum requirements for weld deposits produced from ENiCrMo-6 welding electrodes have been an ultimate tensile strength of 620 MPa and a corresponding elongation of at least 35, three fissures not greater than 0.24 cm during bending and a 33.9 Joule Charpy V-Notch strength at -160.degree. C. with a 0.09 cm minimum mean elongation. Composition of weld deposit requirements arising from welding with ENiCrMo-6 electrodes are given in Table 1 below in weight percent.
TABLE 1 ______________________________________ Element Min. Aim Max. ______________________________________ C -- 0.08 0.10 Mn 2.0 2.5 4.0 Fe 4.0N 10.0 S 0.02 Si 0.7N 1.0 Cu 0.50 Ni 55.0N 70.0N Cr 12.0 14.0N 17.0 Mo 5.0 7.0N 9.0 Cb + Ta 0.5 1.6 2.0 W 1.0 1.6 2.0 P 0.03 Others 0.35N 0.50 ______________________________________ N = Nominal
Commercially available ENiCrMo-6 welding electrodes have been used to weld nickel steel used for cryogenic applications. Typically, ENiCrMo-6 welding electrodes have used an essentially pure nickel core wire such as nickel alloy 200 surrounded by a flux. The problem with commercially available welding electrodes has been marginal out-of-position operability and gross porosity when welding in the overhead position.
It is the object of this invention to produce a base alloy for facilitating welding of close tolerance alloys with reduced porosity in the overhead position.
It is a further object of this invention to produce a nickel steel welding electrode with good out-of-position welding operability.
It is a further object of this invention to produce a welding electrode that reduces porosity when welding in the overhead position.